AD 2020-22-07
Applicability
| Type | Manufacturer | Model | Details |
|---|---|---|---|
| aircraft | Bell Helicopter Textron Inc. | 412 | Airworthiness Directives; Bell Textron Inc. (Type Certificate Previously Held by Bell Helicopter Textron Inc.) Helicopters |
| aircraft | Textron | Inc | Airworthiness Directives; Bell Textron Inc. (Type Certificate Previously Held by Bell Helicopter Textron Inc.) Helicopters |
| aircraft | Bell | Textron Inc | Airworthiness Directives; Bell Textron Inc. (Type Certificate Previously Held by Bell Helicopter Textron Inc.) Helicopters |
Unsafe Condition
excessive pylon pitch vibrations likely caused overload that resulted in cracked main gearbox (MGB) support case failures, and investigations are ongoing to determine the root cause of these vibrations.
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Required Actions
revising Section 2, Normal Procedures, under both ``BEFORE TAKEOFF'' and ``IN-FLIGHT OPERATION(S)'' of the existing Rotorcraft Flight Manual (RFM) for your helicopter to add a caution about what to do if a sudden increase in one-per-rev vertical vibrations occurs with large steady state forward cyclic displacements in combination with collective input while at a certain RPM % is encountered while any part of the skids is touching the ground.
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Compliance Time
Before further flight
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Affected Aircraft
Bell Textron Inc. Model 412, 412CF, and 412EP helicopters
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Source: Official FAA Source ↗
Retrieved: Apr 4, 2026
Rights: U.S. Government Public Domain
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